In the past two decades, a large number of studies have investigated the relationship between biodiversity and ecosystem functioning, most of which focussed on a limited set of ecosystem variables. The Jena Experiment was set up in 2002 to investigate the effects of plant diversity on element cycling and trophic interactions, using a multi-disciplinary approach. Here, we review the results of 15 years of research in the Jena Experiment, focussing on the effects of manipulating plant species richness and plant functional richness. With more than 85,000 measures taken from the plant diversity plots, the Jena Experiment has allowed answering fundamental questions important for functional biodiversity research. First, the question was how general the effect of plant species richness is, regarding the many different processes that take place in an ecosystem. About 45% of different types of ecosystem processes measured in the ‘main experiment’, where plant species richness ranged from 1 to 60 species, were significantly affected by plant species richness, providing strong support for the view that biodiversity is a significant driver of ecosystem functioning. Many measures were not saturating at the 60-species level, but increased linearly with the logarithm of species richness. There was, however, great variability in the strength of response among different processes. One striking pattern was that many processes, in particular belowground processes, took several years to respond to the manipulation of plant species richness, showing that biodiversity experiments have to be long-term, to distinguish trends from transitory patterns. In addition, the results from the Jena Experiment provide further evidence that diversity begets stability, for example stability against invasion of plant species, but unexpectedly some results also suggested the opposite, e.g. when plant communities experience severe perturbations or elevated resource availability. This highlights the need to revisit diversity–stability theory. Second, we explored whether individual plant species or individual plant functional groups, or biodiversity itself is more important for ecosystem functioning, in particular biomass production. We found strong effects of individual species and plant functional groups on biomass production, yet these effects mostly occurred in addition to, but not instead of, effects of plant species richness. Third, the Jena Experiment assessed the effect of diversity on multitrophic interactions. The diversity of most organisms responded positively to increases in plant species richness, and the effect was stronger for above- than for belowground organisms, and stronger for herbivores than for carnivores or detritivores. Thus, diversity begets diversity. In addition, the effect on organismic diversity was stronger than the effect on species abundances. Fourth, the Jena Experiment aimed to assess the effect of diversity on N, P and C cycling and the water balance of the plots, separating between element input into the ecosystem, el...

The natural world is increasingly defined by change. Within the next 100 years, rising atmospheric CO 2 concentrations will continue to increase the frequency and magnitude of extreme weather events. Simultaneously, human activities are reducing global biodiversity, with current extinction rates at B1,000 Â what they were before human domination of Earth's ecosystems. The co-occurrence of these trends may be of particular concern, as greater biological diversity could help ecosystems resist change during large perturbations. We use data from a 200-year flood event to show that when a disturbance is associated with an increase in resource availability, the opposite may occur. Flooding was associated with increases in productivity and decreases in stability, particularly in the highest diversity communities. Our results undermine the utility of the biodiversity-stability hypothesis during a large number of disturbances where resource availability increases. We propose a conceptual framework that can be widely applied during natural disturbances.

Little is known about the role of plant functional diversity for ecosystem-level carbon (C) fluxes. To fill this knowledge gap, we translocated monoliths hosting communities with four and 16 sown species from a long-term grassland biodiversity experiment ('The Jena Experiment') into a controlled environment facility for ecosystem research (Ecotron). This allowed quantifying the effects of plant diversity on ecosystem C fluxes as well as three parameters of C uptake efficiency (water and nitrogen use efficiencies and apparent quantum yield). By combining data on ecosystem C fluxes with vegetation structure and functional trait-based predictors, we found that increasing plant species and functional diversity led to higher gross and net ecosystem C uptake rates. Path analyses and light response curves unravelled the diversity of leaf nitrogen concentration in the canopy as a key functional predictor of C fluxes, either directly or indirectly via LAI and aboveground biomass.

Background and aims Soil hydraulic properties drive water distribution and availability in soil. There exists limited knowledge of how plant species diversity might influence soil hydraulic properties. Methods We quantified the change in infiltration capacity affected by soil structural variables (soil bulk density, porosity and organic carbon content) along a gradient of soil texture, plant species richness (1, 2, 4, 8, 16 and 60) and functional group composition (grasses, legumes, small herbs, tall herbs). We conducted two infiltration measurement campaigns (May and October 2012) using a hood infiltrometer. Results Plant species richness significantly increased infiltration capacity in the studied grasslands. Both soil porosity (or inversely bulk density) and organic carbon played an important role in mediating the plant species richness effect. Soil texture did not correlate with infiltration capacity. In spring 2012, earthworm biomass increased infiltration capacity, but this effect could not be attributed to changes in soil structural variables. Conclusions We experimentally identified important ecological drivers of infiltration capacity, suggesting complex interactions between plant species richness, earthworms, and soil structural variables, while showing little impact of soil texture. Changes in plant species richness may thus have significant effects on soil hydraulic properties with potential consequences for surface run-off and soil erosion

The diversity–stability hypothesis states that current losses of biodiversity can impair the ability of an ecosystem to dampen the effect of environmental perturbations on its functioning. Using data from a long-term and comprehensive biodiversity experiment, we quantified the temporal stability of 42 variables characterizing twelve ecological functions in managed grassland plots varying in plant species richness. We demonstrate that diversity increases stability i) across trophic levels (producer, consumer), ii) at both the system (community, ecosystem) and the component levels (population, functional group, phylogenetic clade), and iii) primarily for aboveground rather than belowground processes. Temporal synchronization across studied variables was mostly unaffected with increasing species richness. This study provides the strongest empirical support so far that diversity promotes stability across different ecological functions and levels of ecosystem organization in grasslands.

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[1] We describe the ecohydrology of a unique semiarid broadleaf deciduous forest in Dhofar (Oman). The forest is surrounded by desert and is confined to a coastal area, where the summer wet season is characterized by a persistent dense cloud immersion. Using field observations, we show how clouds render the ecosystem particularly water conserving and therefore create a niche for a moist forest biome in a semiarid area in three ways. First, horizontal precipitation (collection of cloud droplets on tree canopies) added valuable water, such that about two times as much water was received below the canopy (net precipitation) compared to above (rainfall). Second, high stemflow, of about 30% to net precipitation, led to concentrated water input around the stems. Third, transpiration was suppressed during the cloudy summer season, which allowed for storage of the received water. It was only used after the end of the wet season and lasted for the following 3 months, which roughly doubled the length of the growing season. Our results demonstrate that cloud immersion may shape ecosystem hydrology in significant ways, particularly in semiarid environments.

Soil water content is a key variable for biogeochemical and atmospheric coupled processes. Its small-scale heterogeneity impacts the partitioning of precipitation (e.g., deep percolation or transpiration) by triggering threshold processes and connecting flow paths. Forest hydrologists frequently hypothesized that throughfall and stemflow patterns induce soil water content heterogeneity, yet experimental validation is limited. Here, we pursued a pattern-oriented approach to explore the relationship between net precipitation and soil water content. Both were measured in independent high-resolution stratified random designs on a 1-ha temperate mixed beech forest plot in Germany. We recorded throughfall (350 locations) and stemflow (65 trees) for 16 precipitation events in 2015. Soil water content was measured continuously in topsoil and subsoil (210 profiles). Soil wetting was only weakly related to net precipitation patterns. The precipitation-induced pattern quickly dissipates and returns to a basic pattern, which is temporally stable. Instead, soil hydraulic properties (by the proxy of field capacity) were significantly correlated with this stable soil water content pattern, indicating that soil structure more than net precipitation drives soil water content heterogeneity. Also, both field capacity and soil water content were lower in the immediate vicinity of tree stems compared to further away at all times, including winter, despite stemflow occurrence. Thus, soil structure varies systematically according to vegetation in our site. We conclude that enhanced macroporosity increases gravity-driven flow in stem proximal areas. Therefore, although soil water content patterns are little affected by net precipitation, the resulting soil water fluxes may strongly be affected. Specifically, this may further enhance the channelling of stemflow to greater depth and beyond the rooting zone